Air filter



FIG. 1 is a upper perspective view of the air filter of the present invention;

FIG. 2 is a lower perspective view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a left side view thereof, the right side view being a mirror image thereof; and,

FIG. 6 is a top view thereof, the bottom view being a mirror image thereof.

The features shown in broken lines depict environmental structure only and form no part of the claimed design. 

The ornamental design for an air filter, as shown and described. 